Racemic bupivacaine is an effective long-acting local anaesthetic, and may be given as an epidural. However, racemic bupivacaine is cardiotoxic, having depressant electrophysiological and mechanical effects on the heart. It should therefore be used with caution in cardiac-compromised patients, and the use of high doses and high concentrations is contraindicated.
In particular, bupivacaine has produced death in a number of patients, including women in childbirth and when used in the Bier's block technique. Although the incidence of death has been relatively small, the concern has been sufficient to stop the use of 0.75% bupivacaine for obstetrics and the proscribing of bupivacaine for use in Bier's blocks.
In addition, due to its mode of action, directly on the nervous system, at higher doses, bupivacaine is known to have undesirable central nervous system (CNS) side-effects which, prima facie, are connected to its anaesthetic activity. Indeed, the occurrence of CNS side-effects is one of the major factors limiting the use of this drug in normal clinical practice employing techniques such as local infiltration, nerve block, field block, epidural and spinal blocks.
It has been suggested that levobupivacaine is less cardiotoxic than dextrobupivacaine and racemic bupivacaine. See, for example, Vanhoutte et al., Br. J. Pharmacol. 103:1275-1281 (1991), and Denson et al, Regional Anaesthesia, 17:311-316 (1992). However, these reports are based on work in vitro, and cannot necessarily be extrapolated to any mammals, and certainly not to humans.
The surprising and effective utility of levobupivacaine in man, in vivo, is evidenced for the first time in WO-A-9510276, WO-A-9510277 and Gristwood et al, Exp. Opin. Invest. Drugs 3(11):1209-12 (1994).
An effective, safe, long-acting anesthetic would be particularly valuable for use in facial surgery. However, the administration of such a compound for local anesthesia, and post-operative analgesia, presents particular problems; small volume should be administered, owing to the mass of nerves and/or blood vessels, e.g. around the eyes and in the gums. This is associated with low efficacy. High drug concentrations are therefore necessary.
Lignocaine is widely used, especially in dentistry. However, it is associated with neurotoxicity. In order to give adequate depth of block and duration of action, it is usually administered together with epinephrine. This gives rise to further undesirable effects such as palpitations and syncope. A safer drug would be desirable.